Experimental Study On The Working Characteristics About Two-Pile Composite Foundation

China is a huge geographical country, with the widespread soft foundation and plenty of poor geological condition. Mostly, the soft foundation of the modern high-speed railway is strengthened with pile CFG in order to meet the demands of the intensity,deformation and seismic resistance of the foundation. So, it is necessary to analyze the main factors which effect the settlement and working mechanism of pile CFG's composite foundation. Particularly, the pile-plank structure two-pile composite foundation is still under experimental study and its theoretical research falls behind the practice. So it needs further research and development. Supported by the test for New Ying Kou station in DK217+241.66-DK219+500,a section of the passenger dedicated line from Harbin to Dalian,which is also a scientific research project, this thesis shows that staggered triangular arrangement mode can be used to strengthen the soft foundation. In order to have a better guidance to the engineering practice and provide a reasonable value range for that kind of composite foundation, this thesis dose some research on the co-working mechanism of the pile-soil of the pile-plank structure two-pile composite foundation in following aspects.First, pile-soil stress ratio and composite modulus are the key to the design composite foundation. This thesis analyses systematically about the current pile-soil stress ratio of associated parameter of composite foundation,the bearing capacity of the composite foundation the way to calculate composite modulus and the way to calculate and design the sedimentation.Second, dependent on the field test of composite foundation, this thesis introduces something briefly about the test,the design of the foundation and the arrangement of the components on the testing section. The main testing results are listed and the analysis and comparison of the pile-soil stress,pressure from the deep layer soil,the result of the stress as well as the strain state and settlement of the pile are also presented. From it we can draw some rules about the interaction of pile-soil of the pile-plank structure bi-pile composite foundation, which testify and rich the current theory of composite foundation.Third, according to the construction condition, PLAXIS, the finite element software, is used to do the numerical simulation of plane layout of the piles, which are in the design of composite foundation of rigid long piles and soft short piles. With the comparison between it and the testing result on the spot, the validity and soundness can be verified.Fourth, a comparative analysis is made about the pile-soil stress of composite foundation and the feature of settlement and deformation by researching on the length of pile CFG of bi-pile composite foundation made by the rigid-soft staggered arrangement, the length of MIP, the pile spacing, the thickness of armored concrete slab and the thickness variation of the cushion, along with the help of PLAXIS, the finite element method. From it, a summery about the force-transfer traints of composite foundation assembled by the rigid and soft piles is reached, and the reasonable Values ranges about the length of rigid piles and soft piles, the thickness of armored concrete slab and cushion are also made out. These reasonable Values ranges provide reference for the optimal design of composite foundation of rigid long piles and soft short piles controlled by the settlement in practical.